Some years ago a friend and I went into central London to shoot some
camcorder footage of CCTV cameras for an amateur drama film we planned to make.
Within a few minutes two police cars drove up and armed police politely yet
firmly quizzed us about who we were (name, address, phone number), what we were
doing, where else we'd been filming, whether we supported "the Irish cause" (did
they really expect us to say "yes, we're IRA members planning an attack"?).

Of course we answered all their questions. It's difficult to stick to your
principles when surrounded by people with big guns. My one act of defiance was
to leave the camera switched on, albeit pointing downwards, so that everything
said was recorded.

During the interrogation one officer was on the radio and once he'd
determined we were harmless (a bit insulting really) they sent us on our way -
with a strict warning that if we wanted to film CCTV cameras in future we needed
written permission. Otherwise, next time it might be "the anti-terrorist lot"
who stopped us and we *wouldn't* like that...

We abandoned the film permanently and went straight to the nearest
pub.